Of the various methods of producing tungsten carbide, carburization of tungsten metal through the addition of controlled amounts of carbon black is preferred. Control of the carbon black content permits the production of stoichiometric tungsten carbide with a fractional excess of free carbon. Carbon deficiency is unfavorable as it results in the formation of the brittle eta (η) phase in the final sintered product. Carburization is administered in the presence of hydrogen in a temperature range of 1400 to 2600° C. Temperature of the carburization process is closely controlled and generally kept as low as practical to avoid excessive grain growth in the formed tungsten carbide. The resulting carburized cake is subjected to milling and sieving operations to provide tungsten carbide powder of suitable particle size for combination with other powder species in the production of various grade powders.
Grade powders, for example, can include tungsten carbide mixed with metallic binder and/or additions of other transition metal carbides such as titanium carbide, tantalum carbide and niobium carbide. A mixture of tungsten carbide and metallic binder is subjected to rigorous milling to fracture large carbide crystallites and to distribute the metallic binder throughout the carbide composition. Milling is typically administered with a ball mill or attritor wherein organic liquid or solvent is used to prevent oxidation of the carbide. Organic solvent of acetone or heptane, for example, can be added to the milling drum or attritor tank for oxidation prevention. Employment of organic liquids or solvents can complicate the milling process as such liquids can be flammable and require onerous handling protocols. Further, organic liquid must be removed after completion of the milling, thereby requiring additional processing steps and cost for the production of grade powders.